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L Czer

Publications and source records attributed to L Czer.

6 recordsLinked to original sources
PubMed1992

Effect of prosthetic aortic valve design on the Doppler-catheter gradient correlation: an in vitro study of normal St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves.

To evaluate the normal range of Doppler-derived velocities and gradients, their relation to direct flow measurements and the importance of prosthetic valve design on the relation between Doppler and catheter-derived gradients, five sizes of normal St. Jude bileaflet, Medtronic-Hall tilting disc, Starr-Edwards caged ball and Hancock bioprosthetic aortic valves were studied with use of a pulsatile flow model. A strong linear correlation between peak velocity and peak flow, and mean velocity and mean flow, was found in all four valve types (r = 0.96 to 0.99). In small St. Jude and Hancock valves, Doppler velocities and corresponding gradients increased dramatically with increasing flow, resulting in velocities and gradients as high as 4.7 m/s and 89 mm Hg, respectively. The ratio of velocity across the valve to velocity in front of the valve (velocity ratio) was independent of flow in all St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves when the two lowest flow rates were excluded for Hancock valves. Although Doppler peak and mean gradients correlated well with catheter peak and mean gradients in all four valve types, the actual agreement between the two techniques was acceptable only in Hancock and Medtronic-Hall valves. For St. Jude and Starr-Edwards valves, Doppler gradients significantly and consistently exceeded catheter gradients with differences as great as 44 mm Hg. Thus, Doppler velocities and gradients across normal prosthetic heart valves are highly flow dependent. However, the velocity ratio is independent of flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗
PubMed1992

Color Doppler regurgitant characteristics of normal mechanical mitral valve prostheses in vitro.

BACKGROUND: To evaluate normal regurgitant characteristics of St. Jude (SJ) and Medtronic-Hall (MH) mitral valves, four sizes (25-31 mm) of each were studied in a pulsatile flow model. METHODS AND RESULTS: Regurgitant flow was measured by flowmeter at left ventricular pressures of 80, 130, and 180 mm Hg. Peak regurgitant flow rates ranged from 6.2 to 12.7 cm3/sec in SJ valves and from 7.9 to 17.5 cm3/sec in MH valves. Regurgitant orifice areas calculated from the Doppler continuity equation ranged from 1.6 to 2.0 mm2 in SJ valves and from 2.2 to 2.9 mm2 in MH valves. Regurgitant volumes across the closed valve at a left ventricular pressure of 130 mm Hg were normalized to an ejection time of 280 msec and ranged from 1.5 to 1.9 cm3 in SJ valves and from 2.1 to 2.8 cm3 in MH valves. Jets were imaged by color Doppler in six rotational planes, and jet size and morphology were compared with those of regurgitant jets from circular orifices with sizes comparable to the calculated prosthetic valve regurgitant orifices (1.1-3.1 mm2). SJ valves showed two converging jets from the pivot points, one central jet, and a variable number of peripheral jets. The mean color jet area derived from the six image planes ranged from 1.6 to 5.3 cm2. Aliasing occurred only close to the valve (maximal distance 0.5-2.0 cm). MH valves showed a large central jet with a maximal length of aliased flow between 2.0 and 5.5 cm. Depending on valve size, driving pressure, and image plane, one or two small peripheral jets were found. These jets did not show aliasing in any case. The mean color jet area ranged from 5.1 to 11.0 cm2. Jets originating from circular orifices of comparable size showed jet areas from 5.5 to 13.9 cm2 and aliasing distances from 3.3 to 7.3 cm. At similar regurgitant orifice areas, driving pressures, and regurgitant flows, the measured color areas and aliasing distances were smallest in SJ valves, larger in MH valves, and largest in simple circular orifices. CONCLUSIONS: Large, complex regurgitant jets can be found in normal closed SJ and MH valves by color Doppler, although regurgitant flow volume is minimal. Jet size and velocity distribution differs markedly between SJ valves, MH valves, and circular orifices, even with comparable driving pressure, regurgitant orifice area, and regurgitant volume. The characteristic patterns of normal regurgitation must be recognized to avoid incorrect diagnoses of pathological regurgitation in SJ and MH prosthetic valves. MH valves should not be removed solely on the basis of a central regurgitant jet with a long aliasing distance. Peripheral jets in MH valves and all jets in SJ valves should be considered normal as long as no or only minimal aliasing is present. In contrast, peripheral jets with significant aliasing may represent strong evidence of pathological regurgitation.

Blood Flow Velocity↗
PubMed1990

Discrepancies between Doppler and catheter gradients in aortic prosthetic valves in vitro. A manifestation of localized gradients and pressure recovery.

To evaluate possible causes of discrepancy between Doppler and catheter gradients across prosthetic valves, five sizes (19-27 mm) of St. Jude and Hancock valves were studied in an aortic pulsatile flow model. Catheter gradients at multiple sites distal to the valve were compared with simultaneously obtained Doppler gradients. In the St. Jude valve, significant differences between Doppler and catheter gradients measured 30 mm downstream from the valve were found: Doppler gradients exceeded peak catheter gradients of 10 mm Hg or more by 81 +/- 35% (15 +/- 3.6 mm Hg), and mean catheter gradients by 71 +/- 11% (10.3 +/- 2.5 mm Hg). When the catheter was pulled back through the tunnel-like central orifice of the valve, high localized gradients at the valve plane and significant early pressure recovery were found. When the catheter was pulled back through the large side orifices, gradients at the same level were only 46 +/- 6% of the central orifice gradients (mean difference, 7.6 +/- 4.5 mm Hg). Doppler peak and mean gradients showed excellent agreement with the highest central orifice catheter gradients (mean difference, 1.0 +/- 3.1 and 0.9 +/- 1.5 mm Hg, respectively). A significantly better agreement between Doppler and catheter gradients at 30 mm was found for the Hancock valve, although Doppler peak and mean gradients were still slightly greater than catheter gradients. Doppler gradients exceeded catheter gradients by 18 +/- 10% (3.4 +/- 1.9 mm Hg) and 13 +/- 11% (2.1 +/- 0.9 mm Hg), respectively. When the catheter was pulled back through the valve, the highest gradients were found approximately 20 mm distal to the valve ring.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Cardiorespiratory monitoring in postoperative patients: I. Prediction of outcome and severity of illness.

An index for prediction of outcome for use as a measure of the severity of illness was developed by a nonparametric multivariate analysis of cardiorespiratory data from 113 critically ill postoperative general surgical patients. This severity (predictive) index was based on a computerized algorithm that compares a given observed value with the frequency distributions of survivors and nonsurvivors. The difference in the mean values of this index for survivors and nonsurvivors was statistically significant (p less than 0.001) during each stage of shock. Sensitivity of the index in prediction of survival ranged from 70-93% depending upon stage, the specificity of the index ranged from 76-92%, and the predictive accuracy ranged from 87-96%. The severity index is used as a process measure to track the course of critically ill patients and to evaluate the efficacy of alternative therapies.

Cardiovascular System↗
PubMed1979

Cardiorespiratory monitoring in postoperative patients: II. Quantitative therapeutic indices as guides to therapy.

Immediate (proximate) and late (optimal) therapeutic goals for critically ill postoperative general surgical patients were based on the frequency distributions of cardiorespiratory data of the survivors immediately after resuscitation and in the late stage of shock, respectively. An algorithm was developed which expresses in quantitative terms the distance from observed values for each variable to both of these therapeutic goals. Further, composite indices were also made of related cardiorespiratory variables that reflect the important aspects of acute circulatory failure and its therapy; i.e., volume, flow, tissue perfusion, oxygen transport, and bodily response to stress. The therapeutic indices of nonsurvivors were found to have greater mean deficits that survivors (p less than 0.05) during all but the middle stage of shock. The therapeutic indices greatly aid in the organization and display of monitored cardiorespiratory variables by expressing the circulatory defects in easily understood indices that can be related to therapeutic interventions. Moreover, the interactions of the various aspects of cardiorespiratory function before and after therapy may be easily observed.

Cardiovascular System↗